The theory for a light-emitting diode (LED) to emit light is based on that when a forward voltage power is applied to a p-n junction, the electrons are driven from the n-type semiconductor and the holes are driven from the p-type semiconductor to combine and emit light. The forward voltage power needed is usually supplied by an external power through the p-type and n-type electrodes via conductive wires connected thereto.
As shown in FIG. 1, a known light-emitting diode 101 is set on a carrier 10, and a p-type electrode 104 is electrically connected to the conductive electrode 107 on the carrier 10 via the conductive wire 103, and an n-type electrode 105 is electrically connected to the conductive electrode 106 on the carrier 10 via the conductive wire 102.
FIG. 2A and FIG. 2B illustrate the top views of the structures of light-emitting diodes in parallel (FIG. 2A) and in series (FIG. 2B) connection respectively. A plurality of light-emitting diodes 21 which are the same as the ones shown in FIG. 1 are set on the carrier 20. When a parallel connection is necessary, the light-emitting diodes 21 are electrically connected to conductive electrodes 220, 221 on the carrier board 22 respectively by the conductive wires as shown in FIG. 2A. When a series connection is necessary, as shown in FIG. 2B, the electrodes of different polarity of adjacent light-emitting diodes 21 are electrically connected in series with the conductive wires, and the other two electrodes of different polarity are electrically connected to conductive electrodes 220, 221 on the carrier board 22 to make the light-emitting diodes form a series connection.
It is conventional to use the method illustrated in the FIGS. 2A and 2B to make light-emitting diodes in parallel or series connection. But as the number of the light-emitting diodes to be connected increases, the number of the conductive wires used for soldering also increases. Therefore, the possibility of wires broken during the package process also rises so the devices fail easily. Moreover, no matter for parallel or serial connections, every electrode needs a wire for soldering, and since the size of light-emitting diode is very small, a precise control is necessary for a wire-soldering machine to move back and forth to align and solder, and the throughput of a wire-soldering machine is therefore limited.
FIG. 3 shows another structure for light-emitting diodes connected in series. A plurality of light-emitting diodes 31 is set on the carrier 30, and each light-emitting diode 31 has a p-type electrode 315 and an n-type electrode 316. The light-emitting diode structure 3 is covered by a dielectric layer 32, but the p-type electrode 315 and the n-type electrode 316 are exposed. A conductive layer 33 is laid on the dielectric layer 32 to connect the p-type electrode 315 of one light-emitting diode 31 to the n-type electrode 316 of another light-emitting diode 31 to form a series connection.
Although using the conductive layer 33 on a light-emitting diode chip to connect the electrodes can avoid the prescribed disadvantage of in wire-soldering method, different designs are required for different type of series or parallel connections, and the chips can not be universally and effectively used.